Variable limit stop mechanism



June 28, 1960 UGGETT ETAL 2,942,482

VARIABLE LIMIT STOP MECHANISM Filed Jan. 30, 1959 CAVITY DIFFERENTIALGEARING TO ONE OR MORE SIMILAR DRIVES.

TRIMMER 0R 5 SUBSIDIARY CONTROL MAN RANGE OR TUNlNG CONTROL M 2 Huvmvroxs,

JOHN A. L/GGETT 8 FREQUENCY Y JOSEPH E MC SPAR/PAN. 22% fi fw zfi AT'TORNEX VARIABLE LIMIT STOP MECHANISM John A. Liggett, Haddonfield, andJoseph F. McSparran, Westmont, NJ, assignors to the United States ofAmerica as represented by the Secretary of the Army Filed Jan. 30, 1959,set. No. 190,309

6 Claims. 01. 74-10.2)

This invention relates to shaft positioning means, and more particularlyto apparatus for facilitating coarse and fine adjustment of the tuningmechanism of electronic components.

The objects of the present invention are to provide improved andsimplified shaft positioning apparatus for automatically limiting theoperating range of a subsidiary device whose limits of operation arevaried either manually or by some external driving means as a functionof a physical quantity, such as time. Other features and advantages ofthis invention will be apparent from the fol lowing description taken inconnection with theaccom panying drawings, in which:

Figure 1 is a plan view of a shaft positioning apparatus embodying thisinvention; and

Figure 2 is a graph showing the eifect of the shaft'rotation on thefrequency change of the .driven electronic component.

Rotary limit stops are used in many devices to protect parts such aslead screws, contacts, gears, and several others from damage. Inelectronic devices, the limit stops are often utilized to restrict thetuning range of different resonant circuits. The present invention isparticularly concerned with the utilization of these known rotary limitstops in a novel combination of shaft positioning apparatus for tuningultra-high frequency cavity resonators. The preferred mechanismembodying the principles of this invention comprise a main range ortuning control geared to several interrelated driven devices and tosubsidiary controls or trimmers having on their shafts two sets of limitstops for controlling the rotation thereof in opposite angulardirections; the main control and the trimmers are mechanically coupledto the driven device through a differential or epicyclic gear.

In Figure 1, a cavity resonator 25 is tuned by a slug 24 fixedly securedat one end thereof to bevel gear 23; any suitable type of securing meanscould be employed to fix the gear to the end of slug 24. The teeth ofthe bevel gear 23 are adapted to be driven by the idler bevel gear 22rotatably mounted on the ofiset portion 6' of the trimmer shaft 6. Theidler gear 22 is in turn adapted to be rotated by the bevel gear 21fixedly secured to gear 20 and rotatably mounted therewith upon shaft 6.Gear 20 is driven by gear 32, fixed on the driving shaft 33, withknob 1. Two collars 7 and 13 fastened to shaft 6 by set-screws 8 and 14,respectively carry conventional tumbler stop washers 9 having radiallyand axially projecting fingers 31, the function of which will bedescribed later. Collars 7 and 13 are mounted on shaft 6 above and belowgear 112, as shown. Gear 12 is rotatably mounted on shaft 6.

Trimmer control knob 5, securely fastened to shaft 6, cannot be turnedin either direction when the parts are in the positions shown inFigure 1. Rotation of the knob in the counterclockwise direction, arrow27, is prevented by the restraint on collar 7 caused by the pileup ofstop washers 9 against an outwardly projecting stop shoulder 1 or lug 11of radially mounted rotary stop member 19 securely fastened to gear 12.The rotation of gear 12 is in turn controlled by the main range ortuning control knob 1.

Trimmer control knob 5 cannot be turned in the clockwise direction,arrow 28, due to the restraint on collar 13 caused by the pileup of stopwashers 9 against stud 17 protruding from a stationary limit stop 16. Afriction load 29 is fastened to the stationary support 16 in order toprovide friction on trimmer shaft 6.

By releasing dial lock 26 and turning the main control knob 1 in aclockwise direction, arrow 30, gear 3 drives gearj12 and stop lug 11 ina counterclockwise direction around shaft 6. The displacement of lug 11allows trimmer control 5 to be turned counterclockwise until 1 the stopwashers 9 again pile up against lug 11. Clearly,

'1 ratio canbe suitably varied for any desired ratio of setting of thetrimmer limit to main control. Also, the number of stop washers 9 oneach collar and the spacing therebetween can be suitably selected forany number of desired stop limits. By allowing an initial space be- 1tween fingers 31 of the stop washers 9 and the limit lugs 11 and 17,any-desired minimum range of control of the trimmer Smay be established.

In operation, the cavity resonator is tuned by slug 24 which is, coupledthru the diiferential gear train to the main control knob 1. Thisselects the desired carrier frequency. Knob 1 drives shaft 33 withattached gears 3 and 32. As previously mentioned, gear 3 drives gear 12to control the limit of movement of trimmer shaft 6 by setting lug 11.The opposite limit of rotation of shaft '6 is determined by lug 17.

Gear 32 drives gear 20 and attached gear 21, which in turn drives gears22. and 23, for shaft .6 is held against rotation by brake 29. As shaft6 is freed by the backing off of lug 11 from the position shown inFigure 1, shaft 6 can now be moved within the limits permitted by stops11 and 17, provided sufficient force is applied to knob 5 to overcomebrake 29. This movement of shaft 6 will drive gear 22 around gear 21 torotate gear 23 and shaft 24. Dial lock 26 may be engaged to preventturning of shaft 33 and gears 32, 20 and 21 during this operation. Inthe actual equipment the main control tunes several cavities which donot track exactly, the precise tuning of each cavity being performed bythe separate trimmers 5 through the differential gear trains.

In Figure 2 the effect of the rotation of the main or trimmer controlson the frequency change of the resonant shaft 6 as the main tuningcontrol approaches the less sensitive end of the tuning range.

The limit stops on the trimming control prevent tuning in a wrongcarrier frequency or the unwanted sideband.

Due to the non-linearity of the tuning curve, it is necessary to havelimit stops which have broad limits at one end, of the frequency bandand narrow limits at the opposite end. These requirements are easilyaccomplished'by the Patented June 28, 1960 vention.

While this invention has been described in conjunction with presentpreferred embodiments thereof, it should be apparent that the inventionis not limited thereto. In particular, gear 12 can be driven by othermeans than those shown in Figure 1, such as geared down synchronousmotors, etc. The limits on the trimmer control would then be set withrespect to other functions, such as time. Moreover, the driven devicecould be any electrical or mechanical component such as variableinductors, otentiometers, capacitors, etc.

What is claimed is:

l. A control mechanism for varying an adjustable tuning elementincluding, in combination, a first shaft having a first gear mountedthereon; a second shaft disposed parallel to said first shaft and havinga second gear mounted thereon; a first and a second set of stop membersrotatably mounted on said second shaft, the second gear being in meshwith said first gear; a stationary limit stop; a rotary limit stopfixedly secured to said second gear and concentrically mounted therewithupon said second shaft; the rotation of the second shaft in one angulardirection being prevented by the pile up of said first set of stopmembers against said stationary limit stop, and in the opposite angulardirection by the pile up of said second set of stop members against saidrotary limit stop.

2. The control mechanism of claim 1, wherein means are secured on saidfirst shaft for controlling the position of said rotary limit stop.

3. The control mechanism of claim 1, wherein a third gear is fixedlysecured to said first shaft and a fourth gear is rotatably mounted uponsaid second shaft, the third and the fourth gear being in mesh, andmeans me- 4 ohanically coupling said second shaft and said fourth gearto said tuning element.

4. The mechanism of claim 3, wherein said means is a differential gear.

5. The mechanism of claim 4, wherein said tuning element is a cavityresonator.

6. In a control mechanism for monitoring an adjustable element of atuning device, a first shaft for broad tuning of said element having afirst gear mounted thereon; a

second shaft for limited tuning of said element disposed parallel tosaid first shaft; a second gear in mesh with said first gear rotatablymounted on said second shaft; a first and a second set of stop washersrotatably mounted on said second shaft; a stationary limit stop, arotary limit stop fixedly secured to said second gear and concentricallymounted therewith upon said second shaft; the rotation of the secondshaft in one angular direction being prevented by the pileup of saidfirst set of stop washers against said stationary limit stop, and therotation in the opposite angular direction being prevented by the pileup of said second set of stop washers against said rotary limit stop;and a differential gear mechanically coupling said second shaft to saidadjustable element.

References Cited in the file of this patent UNITED STATES PATENTS1,699,785 Geiger Jan. 22, 1929 2,378,941 May June 26, 1945 2,396,714 MayMar. 19, 1946 2,496,456 Elliott Feb. 7, 1950 FOREIGN PATENTS 780,270Great Britain July 31, 1957 921,813 Germany Dec. 30, 1954

